Gnumeric auto-filled a column I didn’t want it to and I saved the change, stupidly. Having an idea that, thankfully for disk fragmentation, previous versions of the file were probably littered all over the place, I used foremost, the gzip magic bytes you provided, to locate all the gzipped files, and grep to find all the ones that were really gnumeric files and all the ones that were a version of mine. Hand reviewing 60 versions later, I rescued the lost data.

Thanks for your post.